If this is really a true story you should be contacting a good lawyer, not asking for advice on a gambling forum
i'd hope that in a court of law they'd obviously know this guy fucked with the contract and appraise the house to determine market value and force him to pay that. Not like you'd give him that big a discount without knowing him. Even if you nailed his daughter's vagina.
check yourself for STDs too. Icing on the cake man.